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Nikon Labophot Microscope

Introduced around the same time as the Optiphot (1978), the Labophot is lower cost and less flexible.
Positioned for labs rather than research, many were configured for phase contrast.

Nikon 221403 Labophot Microscope Parts Only (S1084)

eBay item number: 155061301918
Condition: For parts or not working
Manufacturer: Nikon
Nikon 221403 Labophot Microscope Parts Only (S1084) "No power."

Received 11 July 2022
Base casting broken next to illuminator;
potentiometer broken.

LED conversion - LED illumination

Common (grounded) emitter bipolar transistors are approximately constant current sources.
Labophot and Optiphot use transistors to modulate halogen lamp power
and variable resistors between base and collector for control.
Labophot potentiometers are about 1K Ohms, connected between collector and base,
with halogen lamp between collector and nominal +7 VDC,
to accommodate incandescent lamp behavior:
  • As filament heats, resistance increases.
  • This lowers voltage drop from collector to emitter
    and also current thru resistor to base, reducing power to lamps.
  • 20W halogen lamps start dimly illuminating with nearly 1A current,
    which may be LED maximum.

    Currents were measured using a CA-60 AC/DC clamp.

LEDs behave differently:
  • For the (2N3716) transistor to work as a nearly constant current source,
    reconfigure variable resistor as a voltage divider between +/-Vcc
    with wiper to base, causing negative feedback
    as base-to-emitter voltage increases with current.
  • Selected LED should be bright enough with 1A
    that 0.65V is maximum base Voltage;
    680 Ohms above 1K potentiometer should sufficiently limit current;
    need to determine minimum base drive for useful brightness.
    to establish resistance between 1K potentiometer and ground.
  • LED will drop nearly constant 6V; transistor will dissipate < 1W.
  • Above some voltage threshold, current increases with temperature.
  • this effectively decreases resistance
    increasing transistor collector-emitter voltage and current
    thru collector-base resistance, provoking current runaway.
  • Supply Voltage Vcc droops slightly with increased current,
    providing slight stabilizing negative feedback.
    # Labophot, Optiphot 66 halogen measurements 12 July, 9 Sept 2022
    #             collector base   lamp     base    lamp
    # dial  Vcc     yellow  brown   mA      mA      V
    OFF                             10      0       0
    1       7.6     6.94    .64     770     0       .2
    1.5     7.51    6.9     .64     770     0       .2
    2       7.5     6.6     .65     910     9       .3      # very dim
    2.5     7.36    6       .68     1180    11      .6
    3       7.25    5.3     .70     1520    17      1.2
    3.5     7.19    5       .71     1690    18      1.5
    4       7.12    4.6     .73     1850    22.5    1.85
    4.5     7.06    4       .74     2110    26      2.4
    5       6.95    3.2     .78     2430    34      3.3
    5.5     6.8     2       .81     2870    47      4.5
    6       6.6     0.9     .85     3170    69      5.5   
    
Francisco made an LED replacement similar to my intent.
For 5W LED instead of 20W halogen,
replace 1K variable resistor between 2N3716 collector and base,
which supplies a minimum of 1mA forward bias,
rewiring the potentiometer as a voltage divider with:
  • 680 Ohms in series between CW and +Vcc (about 8VDC),
  • wiper to base, and
  • CCW to -Vcc

  • Fine Focus

    This "parts only" Labophot was 1 of only 2 Nikon finite CF microscope frames received with intact fine focus;
    broken focus on 2 others had split polymer pinion gears;   two lost grip on the shaft flat, for which symptions are:
    • turning fine focus knobs having no effect
    • turning coarse focus knobs having no or inconsistent effect
    • stage settling without knob motion
    • turning coarse focus knob when stage is at a limit NOT provoking fine focus knob spin
    To understand how Labophot/Optiphot stage focus works, first consider a planetary gear set:
    .. and that if either sun or planet gear were not fixed,
      then torque could not be transmitted.

      While a polymer gear can be damaged by exceedingly stiff focus rack
      e.g. from dried grease, damage more surely occurs
      when a user twists fine focus while focus rack is against a stop
      or coarse focus is held by the other hand.
     

    Labophot/Optiphot stage focus employs a single large planetary gear (125) for fine focus:
    not shown above:  plymer washers between both fine and coarse focus knobs, wave washer on gearcase side.
    • a fine focus shaft(111), inside
    • a coarse focus tube(110) to which knob(104) and brass gearcase(107) fasten, inside
    • a pinion gear tube(109) with sun gear(123), driving
    • a stage focus rack(9), where
    • focus shaft and coaxial tubes are connected by sun and planet gears(123-128).
    • The fine focus shaft wave (spring) washer and grease apply resistance to coarse knobs via delrin washers.
    • If/when a fine focus pinion (sun) gear(128) splits or otherwise loses grip on its shaft,
      then the focus (planetary) gear train cannot transmit torque.
    Some Optiphots and Labophots have different fine focus gear trains:
  • 0.2mm per rotation with a single large planetary gear
  • 0.1mm per revolution with an idler gear train
    0.2mm per rotation on left;  0.1mm per rotation on right

    Both employ the same fragile polymer fine focus pinion gear:


    Other Nikon fine focus discussions:

    Lothar Lothman was among the first to sort Labophot pinion gear 3mm bore 18 tooth module 0.3 spec.
    http://www.photomacrography.net:   Some progress in the repair of the Labophot 1

    Single large planetary gear, as in Optiphot-66, wants pinion gear on fine focus shaft within 1mm from brass gearcase.

    Broken plastic fine focus gear topic   <- warning!! too much disassembly for just fine focus gear replacement!
    (but educational images)

    Fine focus pinion gear repair/replacement

    If replacing a Nikon polymer fine focus pinion gear with a narrower metal gear, proper positioning becomes more critical.
    1. loosen (but do not remove) fine focus knob set screws using 1.3mm hex key
    2. remove fine focus knobs without grasping coarse focus grips;
      do NOT attempt to remove left-hand coarse focus or brass planetary gearcase from their threaded tube;
      they are secured with thread locker with tension adjusted for resistance to gravity.
      Polymer threads in left coarse focus knob will be destroyed by unscrewing it.
    3. pry loose thin metal cover that is glued over screws on coarse focus knob
    4. remove 3 screws fastening coarse focus plastic grip to planetary gear case
    5. withdraw fine focus shaft with pinion gear
    6. degrease and dry pinion gear and that end of the fine focus shaft
    7. secure metal pinion gear to shaft (step 8 here) with blue thread locker;  2-part epoxy for polymer pinion gears.
      Nikon's polymer pinion gears are about 6mm wide;
      narrower metal gears must be carefully located to mesh planetary gears:
      • Some tweaking is possible by loosening fine focus knob set screws and sliding knobs on shaft flats;
        additional tweaking by moving wavy washer from one side to the other.
      • Center fine focus shaft flat on end opposite planetary gearcase about 10mm from coarse focus:
      • Pinion gear flat should be about 1mm from gearcase:
      • To fully engage this fine focus idler gear train instead of single large planetary gear,
        narrower metal pinion gear should be spaced about 3mm from gearcase:
      • Before securing pinion gear, move that gear between gearcase and flat
        so that adhesive fluid on flat gets smeared away from the gearcase:
      • Pinion for idler gears should be 18mm from end of fine focus shaft:
      • OK for idler gear train, this pinion gear should be reversed to better engage single large planetary gear:
    8. reinstall fine focus shaft with pinion gear secured
    9. grease pinion gear and wavy washer
    10. reinstall coarse focus plastic grip and metal cover
    11. install fine focus knobs, partially compressing wavy washer and tightening set screws,
      without gripping coarse focus.

    Here is discussion and images for related Nikon MM-11 focus,
    which has a coarse focus tension ring (missing on my Labophot, but present on others).
  • maintained by blekenbleu